Don't use Win32, a lot of things you come to rely on being done for you - namely Live Resize and the like aren't in Win32. Qt's been a bag of hurt for me on my various attempts to use it in Linux and OS X, Windows may be another story.
wxWidgets made me want to kill myself - and that was just reading the documentation
Most of them either suck to use or are ridiculously over implemented, whatever one you pick you'll end up raging after a while. Literally the only app framework I've gotten on well with is Windows Forms, if you still want to code in C++ that's more than possible with Windows Forms, it's just Managed C++, which afaik is just a wrapper around the standard variety.